Oscillator modulator



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OSCILLATOR MODULATOR Filed Jan. 14, 1933 I "21; I 0' 7/9/90 63/0 Vail 16f INVENTOR- HARQLD A.WHEELER Y I PW,$4A-'4.,WMA-J A1TORNEY$ Patented Mar. 17, 1936 UNITED STATES biidi "o PATENT OFFICE OSCILLATOR MODULATOR Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltlne Corporation Application January 14, 1933, Serial No. 651,755

8 Claims.

The present invention relates to oscillatormodulator circuits, and more particularly to such circuits for use with thermionic tubes employing five or more electrodes.

This invention contemplates the operation of a pentode or five-electrode vacuum tube to perform two separate functions, the cathode, suppressor, and plate electrode, considered as a triode, serving to function as an oscillator; and all the electrodes, considered as a pentode, serving to function as a modulator.

Although oscillator-modulator circuits have been developed utilizing a single vacuum tube, very few of those of which the applicant is aware give as stable operation as may be obtained by the use of separate oscillator and modulator tubes. Therefore the simplicity and lower cost obtainable by these combined oscillator-modulator arrangements is in a measure oifset by the lack of complete stability of such systems.

Furthermore, in a radio receiver, in connection with which the present invention is particularly useful, difliculty is frequently experienced in that the oscillation-frequency currents are radiated, causing interference with other receivers in the neighborhood. To prevent this radiation it is generally necessary to employ a uni-directional coupling tube which, except for this use, is unneeded in the receiver, and constitutes an additional expense in the manufacture of the receiver and in its use.

It is the object of the present invention to overcome each of the above-noted objectionable features of the usual system and to produce an improved oscillator-modulator system which shall give greater stability than the ordinary oscillator-modulator systems, while including all the advantages of systems using separate oscillator and modulator tubes.

Another object of this invention is to produce a system which will not cause radiation of the oscillation-frequency current when employed in radio receivers.

These and further objects and advantages of the invention will become apparent from the following specification and claims taken in connection with the accompanying drawing.

In accordance with one embodiment of this invention, the tuned input circuit of the oscillator-modulator is connected between the cathode and control electrode, which in this arrangement is the first or inner grid of a vacuum tube having five or more electrodes. Relative to the screen or second grid, to which a high voltage source is connected, these elements act as an amplifier or, more properly, as a modulator, as will be explained hereinafter. The anode is connected to the tuned intermediate-frequency circuit and is coupled to the oscillation circuit by a uniform gain coupling which is preferably a combined electromagnetic and electrostatic coupling so proportioned as to give a substantially uniform oscillation voltage as the circuits are tuned through a desired frequency band. The oscillation circuit is connected to the third or outer grid of the pentode. This grid which is commonly referred to as the suppressor grid is maintained at a negative potential relative to the cathode of the tube, in order to prevent secondary emission. The anode is connected to a source of potential which is positive relative to the cathode but is preferably less than the potential of the screen or second grid.

In operation, the control grid serves to control the cathode emission, and the voltage of the third grid, which is, as above noted, connected to the oscillation circuit, serves to vary the anode current, but is powerless to affect the cathode emission.

In the accompanying drawing,

Fig. 1 is a circuit diagram showing a pentode arranged to operate as an oscillator-modulator in a superheterodyne radio receiver, and

Fig. 2 is a diagram showing the anode-current third grid-voltage characteristics of the tube used in Fig. 1.

In Fig. 1 a tuned input circuit II is connected between the first or control grid and the cathode of the tube I2. The circuit II is tuned to the desired signal frequency by means of the variable condenser I3. A low-potential battery I4 is provided between the tuned circuit and the cathode of the tube I2 to provide the proper grid bias.

The second or screen grid of the tube I2 is connected to the positive terminal of a high-potential battery I5. A bypass condenser 22 is provided across the battery I5. The anode or feedback circuit, which is connected between the anode of the tube I2 and the cathode thereof, includes the tuned circuit I6, tuned to the intermediate frequency by the condenser II, the coupling inductance I8, coupling condensers 20 and 2|, and bypass condenser 23. The anode potential is supplied by the battery I5 through the ballast resistor I9.

The oscillation circuit 24 comprises the inductance 26 coupled to the inductance I8, the variable condenser 25, by which the circuit is tuned to the oscillation frequency, and the coupling condenser 2I. That point of the oscillation circuit between the inductance 26 and the condenser 25 is connected to the third or suppressor grid of the tube I2, and a negative bias is impressed upon this grid relative to the cathode of the tube I2, through resistor 28, by means of the low-potential i2 iiuviu battery 21 connected to that point of the oscillation circuit between the coupling condenser 2| and the inductance 25.

The condensers I 3 and 25 may be connected, as indicated by the dotted line, for simultaneous operation, in which event the condenser 2| is co properly selected to permit alignment between the two circuits giving a constant diiference or intermediate frequency. The condenser 2| thus has thedual function of acting as a coupling between the feedback or output circuit and the oscillator circuit and of assisting the alignment between these circuits.

Any suitable means are provided for heating the cathode of the tube H such as are common in the art to which this invention pertains.

In the operation of the above-described figure as the oscillator-modulator or first detector of a superheterodyne radio receiver, for instance, the tuned circuit II is tuned by the condenser I3 to the radio input or signal frequency, and the oscillation circuit 24 is simultaneously tuned by the condenser 25 to a frequency differing from the signal frequency by the frequency to which the intermediate-frequency circuit 16 is tuned. The cathode, first grid, and second grid act, under these conditions, as the elements of an ordinary triode, the first grid serving to control the cathode emission and thus the current to the cathode and consequently that passing a point just inside the second grid. The voltage of the third grid, which is, as above noted, connected to the oscillation circuit 24, has for any given value of second-grid and first-grid voltages a differential effect upon thesecond-grid and anode current, as indicated in Fig. 2, to which attention is now invited. As the voltage of the third grid becomes more negative, for instance, the anode current decreases, as shown by curve 30, and simultaneously the current to the second grid, as indicated by curve 3|, increases by a corresponding amount,it being noted that the total of the anode and secondgrid current is substantially constant, as indicated by the curve 32. It is thus seen that the voltage of the third grid has no appreciable effect upon the cathode emission, the latter being controlled substantially entirely by the voltages of the first and second grids. The changes in anode current are fed back to the oscillation circuit through the coupling between the output inductance l8 and the oscillation inductance 26 and through the mutual coupling provided between the output and oscillation circuits by the mutual condenser 2| These two couplings are so adjusted that as the frequency to which the input and oscillation circuits is varied, the variation of electromagnetic transfer between the inductance of i8 and 26 is offset by a corresponding variation in the coupling provided by the condenser 2|.

The following voltages have been found suitable for an oscillator-modulator built in accordance with the above description when using a type '57 pentode. These voltages are merely illustrative and are not to be considered a limitation, it being understood that any appropriate voltages may be applied without departing from the spirit of the invention. The following voltages are relative to the cathode of the tube:

First or control grid=7 Second or screen grid=+278 Third or suppressor grid= 23 Anode=+18l In view of the fact that the voltage of the anode, relative to the second grid, is quite critical, the resistor I! has the dual function of permitting coupling of the output circuit to the tuned oscillation circuit 24 through the condenser 20 and of regulating the average anode voltage. For use with the voltages above given with a type '57 pfizggde this resistor should have a value of 60,000 0 0 It is to be noted that due to the high positive voltage of the second grid, coupling eflects between the third suppressor grid and the first grid are substantially eliminated, and therefore reaction between the oscillation and input circuits is prevented, these circuits being effectively isolated from each other.

It is to be noted also that no secondary emission eifect is experienced within the operating range of the circuit, as might be expected from the fact that the voltage of the anode is less than that of the second grid. This is prevented by the negative voltage of the third grid, as indicated by the range covered by the curve 30 of Fig. 2.

Whereas batteries have been shown for providing the desired potential, it is to be understood that in operation the customary unitary power source can be utilized, care being taken, however, to provide resistors which would permit obtain ing the desired voltages.

- It is to be understood that whereas the invention has been described in connection with a pentode or five-electrode vacuum tube, it is applicable to any tube having a greater number of electrodes, the same general relationship between the spacing of the electrodes and the voltages applied thereto, however, being substantially that used in connection with the pentode arrangeent constituting the present disclosure. What is claimed is:

1. An oscillator-modulator circuit which inlu s a multi-electrode vacuum tube, an input circuit, tuned to the frequency of the current to be modulated, connected to a first pair of electrodes including the cathode of said tube, an oscillation circuit, tuned to the frequency of theEo dfilating current, connected between one of a second pair of electrodes of said tube and said cathode, a source of high positive potential connected to a fifth electrode for isolating said input circuit from the oscillation currents, the potential of said fifth electrode being the highest voltage in the tube, and means for providing a uniform output from said oscillation circuit as the circuits aggtjusnled through a frequency band.

oscillator-modulator circuit which includes a multi-electrode vacuum tube having an inner pair of electrodes including a cathode, an outer pair of electrodes including an anode, and a middle electrode; an input circuit, tuned to the frequency of the current to be modulated, connected to said inner pair of electrodes; an oscillation circuit, tuned to the frequency of the modulating current, connected between one of said outer pair of electrodes and said cathode: a source of high positive potential connected to said middle electrode for isolating said input circuit from the oscillation currents; and means for providing a uniform output from said oscillation circuit as the circuits are tuned through a frequency band.

3. An oscillator-modulator circuit which includes a multi-electrode vacuum tube having an inner pair of electrodes including a cathode, an outer pair of electrodes including an anode, and an intermediate electrode; an input circuit, tuned to the frequency of the current to be modulated and connected to the inner pair of electrodes of said tube; feedback and oscillation circuits connected between the outer pair of electrodes and said cathode, said oscillation circuit being tuned to the frequency of the modulation current; a source of high positive potential connected to the intermediate electrode for isolating said input circuit from said oscillation currents; and means for providing a uniform oscillation voltage as the input and oscillation circuits are timed through a frequency band.

4. An oscillator-modulator circuit which comprises a multi-electrode vacuum tube having an inner pair of electrodes including a cathode, an outer pair of electrodes including an anode, and an intermediate electrode; a tuned input circuit, tuned to the frequency of the current to be modulated, connected to said inner pair of electrodes; an oscillation circuit, tuned to the frequency of the modulating current and coupled to one of the outer pairs of electrodes, of said tube and connected to said cathode; a uniform gain coupling between the anode and said oscillation circuit; and agisource of high positive potential connected to "intermediate electrode, whereby there is produced thbscillator modulator in which reaction between said oscillation and input circuits is prevented.

5. An oscillator-modulator circuit which comprises a multi-electrode vacuum tube having an inner pair of electrodes including a cathode, an outer pair of electrodes including an anode, and an intermediate electrode; a tuned input circuit, tuned to the frequency of the current to be modulated, connected to said inner pair of electrodes; feedback and oscillation circuits connected between said outer pair of electrodes and said cathode; said oscillation circuit being tunable to the frequency of the modulating current; a uniform gain coupling between said feedback and oscillation circuits, and a source of high positive potential connected to the intermediate electrode, whereby there is produced an oscillator modulator in which reaction between said oscillation and input circuits is prevented.

6. An oscillator-modulator circuit which com prises a vacuum tube having cathode, control grid, screen grid, a third grid, and an anode, an input circuit, tuned to the frequency of the current to be modulated, connected between the cathode and control grid, an oscillation circuit, tuned to the frequency of the modulating current, connected to said third grid and said cathode, a feedback circuit connected between said anode and said cathode and coupled to said oscillation circult. and a high positive potential source connected to mid screen grid, whereby there is produced an oscillator-mod tor circuit in which the oscillation current lb isolated from the input circuit, the voltage of said screen grid being higher than that of said anode.

'7. An oscillator-modulator circuit which comprises a vacuum tube having cathode, control grid, screen grid, a third grid, and an anode, an input circuit, tuned to the frequency of the current to be modulated, connected between the cathode and control grid, an oscillation circuit, tuned to the frequency of themodulating current, connected to said third grid and to said cathode, a feed back circuit connected between said anode and said cathode and coupled to said oscillation circuit, and a high positive potential source connected to said screen grid, whereby there is producedan oscillator-modulator circuit in which the oscillation current is isolated from the input circuit, the voltage of said screen grid being higher than that of said anode, and the voltage of said third grid being negative relative to both said cathode and said control grid, whereby the screen-grid current is made greater than the anode current.

8. An oscillator-modulator circuit which comprises a vacuum tube having cathode, control grid, screen grid, a third grid, and an anode, an input circuit, tuned to the frequency of the current to be modulated, connected between the cathode and control grid, an oscillation circuit, tuned to the frequency of the modulating current, connected between said third grid and said cathode, a feedback circuit connected between v said anode and said cathode and coupled to said oscillation circuit, and a high positive potential source connected to said screen grid, whereby there is produced an oscillator-modulator circuit in which the oscillation current is isolated from the input circuit, the voltage of said screen grid being higher than that of said anode and the voltage of said third grid being negative relative to the cathode, whereby the screen-grid current is made greater than the anode current.

HAROLD A. WHEELER.

Pate t No. 2,05 ,01

March 17, 1936.

HARDLD A. WHEELER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 55, strike out the comma after "cathode" and insert instead a semicolon; page 5, first column, line 13,. claim 4, for "pairs" read pair;line 17, same claim, for "an" read the; and line 18, same claim, for "the" read an; second column, line 4, claim 6, for "in" read is; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 28th day of April, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

